When I got my first iPod touch I listened to an audiobook and memorized the minute that I paused.
When I listened to it again I wanted to go there by clicking on the scroll bar,
but the scrollbar did not appear when I clicked on the audio file.
So I had to use the forward button.
To trigger the scrollbar you have to click just on the touch area in the middle,
but I hadn't known this at the beginning.

I think it is not their focus, because normally you don't go to another minute in a song.
You'd rather go to the next song.
So you don't need the scrollbar often.
But when you need it, you are supposed to know how to trigger it.